Abstract Peer influence is one of the most important predictors of alcohol and other drug use in adolescence, and these affiliations often arise when socially marginalized youth self-aggregate and reinforce alcohol use and other deviant activity (i.e., ?deviant peer clustering?). Even though the field has developed efficacious school-based prevention programs, effect sizes are generally small, and these programs can be difficult to disseminate with fidelity and challenging to sustain due to complex designs and the significant time-and-money expenditures required for materials and training. Thus, existing school-based prevention programs have not provided compelling value to schools, which has limited their dissemination. In a recent RCT, we aimed to reduce alcohol use in middle school by exposing at-risk youth to a broader cross-section of the school social network (and interrupting the process of deviant peer clustering) through collaborative, group-based peer learning activities. After one year, we found significantly lower rates of deviant peer affiliation and alcohol and tobacco use in intervention schools as compared to control schools. Peer learning also has moderate-to-strong effects on bullying, victimization, and student engagement and achievement, so peer learning represents a highly attractive approach to alcohol use prevention that can support positive behavioral, social, and academic outcomes simultaneously. However, teachers in our intervention schools encountered a few challenges when implementing peer learning, including: (1) fidelity, i.e., ensuring that peer learning provided the most positive student experience by including all the essential design elements; and, (2) instructional support, i.e., managing the flow and timing of the activities to complete the lesson on time and dealing with unexpected disruptions. Thus, in this Phase I SBIR, we aim to develop a mobile software application that will provide easy-to-use, scalable organizational templates with workflow support that teachers can use to automate the design and delivery of evidence-based peer learning activities. With this app, the teacher will design their lesson by selecting from a library of pre-existing templates for different lesson types which they can customize and populate with their own learning materials as needed. During lesson delivery, the app will manage membership in learning groups (including changes required by late-arriving or absent students), direct student activities according to a specified timetable, manage student work products, support teacher observations of student behavior, and deliver post-lesson content reviews and assessments. The app should be highly attractive to both teachers (for its ease of use, rapid implementation, flexibility, instructional support) and school administrators (for its evidence-based approach to the prevention of a variety of behavioral problems, greater student motivation and achievement). In Phase I, we will focus on the jigsaw lesson, a standard peer learning activity that is widely recognized and accepted. We will develop the app iteratively in conjunction with actual teachers and students, who will use the app in their classrooms and provide feedback to guide development.